1. Field of the Invention
This invention relates to Mn—Al magnetic powders and a manufacturing method thereof, more particularly, Mn—Al magnetic powders of a high coercive force which are obtained from Mn—Al alloy vaporized by plasma arc discharging, and a method for manufacturing the magnetic powders.
2. Description of Related Art
Ferrite magnets or ferrites are generally produced as sintered products using technologies in the powder metallurgy field, and comprise iron oxide as their principal component and barium or strontium depending on their applications.
The ferrites are classified as dry process products using special binding powders and wet process products using water according to making-process, and also as isotropic type and anisotropic type according to the direction of magnetism.
Because of their low price, the ferrites have various applications including speakers, motors, health care equipments, tools for learning, tachometers, TVs, lead switches, watch movements and so on.
The most widely-used type of rare earth magnet is a neodymium magnet. The neodymium magnet is produced by sintering raw materials such as iron oxide, boron, and neodymium which is one of rare earth elements (17 elements: atomic numbers are #21, #39, and #59 to #71), and has a high value of energy product. Typically it has been used in the light, thin, short, and small cutting-edge product.
Japanese patent publication no. 1984-46008 discloses a rare earth magnet manufactured by sintering, and no. 1985-9852 discloses a method for manufacturing rare earth magnets by high speed quenching.
Rare earth magnets have the highest value of energy product (25˜50 MGOe) among the commercialized magnets.
However, the rare earth magnets tend to be vulnerable to corrosion as a shortcoming, since they comprise one or more of rare earth elements and iron which are relatively susceptible to oxidation. Therefore, a protective coating is needed to avoid the surface oxidation, which leads to a higher manufacturing cost.
It is an object of the invention to provide Mn—Al magnetic powders of a high coercive force which are obtained from Mn—Al alloy vaporized by plasma arc discharging, and a method for manufacturing the powders.
It is another object of the invention to provide Mn—Al magnetic powders of light weight and enhanced corrosion resistance, and a method for manufacturing the powders.